You can reinforce your understanding of the objectives covered in this
chapter by opening the interactive media activities on the CD accompanying this
book and performing the lab activities collected in the Cisco Networking
Academy Program CCNP 1: Advanced Routing Lab Companion. Throughout this
chapter, you will see references to these activities by title and by icon. They
look like this:

Interactive Media Activity

Lab Activity

A scalable network requires an addressing scheme that allows for growth.
However, several unanticipated consequences can result from unmanaged network
growth. As new nodes and networks are added to the enterprise, existing
addresses might need to be reassigned. Excessively large routing tables might
slow down older routers, and the supply of available addresses might simply run
out. You can avoid these unpleasant consequences with careful planning and
deployment of a scalable network addressing system.

Network designers can choose from among many different network protocols and
addressing schemes. However, with the emergence of the Internet and its
nonproprietary protocol, Transmission Control Protocol/Internet Protocol
(TCP/IP), this has meant that virtually every enterprise must implement an IP
addressing scheme. In addition to TCP/IP, several proprietary network protocols
and addressing schemes have been used. Companies such as Apple and Novell have
recently migrated their network software to TCP/IP and away from their
proprietary protocols. Presently, many organizations choose to run TCP/IP as the
only routed protocol on the network. The bottom line is that administrators must
find ways to scale their networks by using IP addressing.

Unfortunately, the architects of TCP/IP could not have predicted that their
protocol would eventually sustain a global network of information, commerce, and
entertainment. Twenty years ago, IP version 4 (IPv4) offered an addressing
strategy that, although scalable for a time, resulted in an inefficient
allocation of addresses. Over the past two decades, engineers have successfully
modified IPv4 so that it can survive the Internet's exponential growth.
Meanwhile, an even more extensible and scalable version of IP, IP version 6
(IPv6), has been defined and developed. Today, IPv6 is slowly being implemented
in select networks. Eventually, IPv6 might replace IPv4 as the dominant Internet
protocol.

This chapter explores the evolution and extension of IPv4, including the key
scalability features that engineers have added to it over the years:

Subnetting

Classless interdomain routing (CIDR)

Variable-length subnet masking (VLSM)

Route summarization

Finally, this chapter examines advanced IP implementation techniques such as
the following: